The present invention relates generally to the field of optical fiber connectors, and, more particularly, to an improved method of making V-groove plastic support members for use in optical connectors, including multi-fiber optical connectors.
With the demand for high speed, multi-media services constantly increasing, optical fibers are gaining increased attention as communication service providers design their networks to carry high bandwidth signals. Unfortunately, the precision required in connecting optical fibers together precludes the practice of bundling large numbers of fibers in a single cable as is frequently practiced with copper wires. Instead, fibers are generally organized in a precise, spatial relationship, such as in a ribbon cable, in which the fibers are organized and molded adjacent to one another in a plastic ribbon. Alignment of such fiber arrays either with other arrays or with optical components can be troublesome, especially for the case of single mode fibers, which have an extremely small core diameter (typically around 8 .mu.m).
The multi-fiber connectors used to interconnect fiber arrays typically comprise two plugs of silicon or plastic molded from a silicon template with V-grooves formed therein to seat the individual fibers and alignment pins. Each plug is made from two mated support members that are bonded together to encase the fibers. If the plug is made from silicon, the V-grooves are formed prior to bonding by anisotropically etching a major surface of each support member to match the spatial relationship of the fibers in the array. If the plug is made from plastic, a silicon template is anisotropically etched to form V-grooves corresponding to the fiber array pattern. This template is then used to create a mold insert from which plastic support members can be produced having the necessary arrangement of V-grooves.
Monocrystalline materials, such as silicon, are used in manufacturing support members for optical connectors because etching of these materials inherently progresses along crystallographic planes, which permits features to be formed with precise predictability. In the production of V-groove features in a silicon wafer or substrate, the wafer is coated with a thin (i.e., .about.1 .mu.m thick) layer of a first masking material on both of its major surfaces. The first masking layers may be fabricated, for example, from silicon dioxide or silicon nitride. After the first masking layer has been applied, a conventional photoresist mask is applied, which forms a second masking layer over the silicon. Conventional photolithographic techniques are used to create a pattern of windows in the photoresist in the first major surface of the wafer. After etching the first masking layer to expose the silicon wafer through the pattern of windows, the photoresist is removed. A first masking layer fabricated from silicon dioxide may be etched with a buffered hydrofluoric acid solution. During the oxide etching process on the first major surface, the second major surface is protected by a second masking layer of photoresist, which is stripped after the oxide etching process. Once the photoresist and first masking layer have been etched, the photoresist is stripped from the wafer and the wafer is anisotropically etched with an ethylene diamine pyrocatechol solution to create the desired V-grooves through the windows in the first masking layer. Lastly, the first masking layer is stripped, and the wafer is sectioned into individual V-groove submounts. The silicon exposed through the windows in the first masking layer is typically anisotropically etched to create the desired features (e.g., the V-grooves) that lie in the wafer vicinal (100) crystal plane. Preferably, the V-grooves are aligned parallel to the &lt;110&gt; direction. The planar facets bounding the V-grooves lie within {111} planes that are inclined with respect to the (100) plane at an angle of 54.74.degree.. Similarly, using silicon nitride as the first masking layer, a solution of KOH in water can be used to create the same V-groove features.
One common approach to ensuring a precise alignment between fiber arrays is to etch deeper V-grooves in the silicon surface to serve as alignment grooves. These grooves are used to seat alignment pins or rods or ball lenses or ball bearings that join two connectors together. For the alignment pins or ball bearings to be effective, however, precise control over the placement and the dimensions of the alignment grooves must be maintained during etching. For example, an optical connector may be designed with fiber support members that require lateral symmetry with respect to a center of symmetry be maintained. During the etching process of masked silicon wafers, control over lateral symmetry is most frequently lost when etching the deeper V-grooves that are used for the alignment pins. In addition to compromising the lateral symmetry of the multi-fiber connector, the alignment grooves require significantly more time to etch than the V-grooves holding the individual fibers. Typically, alignment grooves are over six times as deep as the V-grooves holding the fibers thus requiring over four to six times as much time to etch.
Consequently, there is a need for an improved method for producing optical connector support members that provides greater control over the placement and dimensions of etched features (e.g., alignment V-grooves). It is further desired that the improved method use less etching time than has been required heretofore to produce similarly styled connectors.